It is well known that amorphous alloys of various form such as a ribbon, a fine wire, a powder or particle, etc. may be obtained by quenching the alloy in a molten state. Also, hitherto, many amorphous alloys have been identified in Fe-based alloys, Co-based alloys, Ti-based alloys, Zr-based alloys and Al-based alloys. Among these an Fe-based amorphous alloy has excellent soft magnetic characteristics, high strength and good thermal stability. Therefore, Fe-based amorphous alloys have been applied in various industrial fields for use as a transformer material, etc., and have been used to develop new magnetic materials.
However, because a conventional amorphous alloy does not have a sufficient amorphous phase-forming ability and requires a high quenching rate, the use of such a conventional Fe-based amorphous alloy is limited to forming a ribbon having a thickness of 60 .mu.m or lower, a fine wire having a diameter of 150 .mu.m or lower, or a powder having a particle size of 100 .mu.m or lower. As a result, the industrial use thereof has been limited.
On the other hand, JP-A-5-245597 and JP-A-5-253656 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") propose casting method using a mold (hereinafter referred to as a mold casting method), and disclose a method of obtaining a casting of an Fe-based amorphous alloy. However, in the case of using conventional Fe--Si--B based alloys and Fe--P--C based alloys, a thick bulk-form amorphous material is not obtained. This limitation hinders the development of new applications for Fe-based amorphous alloys.
In view of the above, Fe-based alloys having an excellent amorphous phase-forming ability have recently been investigated, and an alloy having the compositional formula Fe.sub.72 Al.sub.5 Ga.sub.2 P.sub.11 C.sub.6 B.sub.4 which exhibits a wide supercooled liquid region of 50 K or larger has been found as described in Material Transactions, JIM, Vol. 36, No. 9, 1180-1183 (1995). This alloy has an excellent amorphous phase-forming ability as well as excellent soft magnetic characteristics and excellent thermal stability, and was therefore expected to provide a functional amorphous alloy bulk material.
However, the present inventors found that when a casting having a thickness of 1.5 mm or above of the foregoing Fe.sub.72 Al.sub.5 Ga.sub.2 P.sub.11 C.sub.6 B.sub.4 alloy is produced by the mold casting method disclosed in JP-A-5-245597, the amorphous phase-forming ability is insufficient and a casting material having an amorphous single phase is not obtained.
Accordingly, the development of an Fe-based amorphous alloy having a superior amorphous phase-forming ability which can be produced in a bulk-form having a thickness of 1.5 mm or above has been desired. Also, in order not to reduce its workability, the amorphous alloy should have a wide supercooled liquid region of 50 K or larger in addition to an excellent amorphous phase-forming ability. From this view point, the development of an Fe-based amorphous alloy having an amorphous phase-forming ability that is superior to that of the Fe.sub.72 Al.sub.5 Ga.sub.2 P.sub.11 C.sub.6 B.sub.4 alloy and a wide supercooled liquid region has been desired.